The present invention relates to apparatus for removably connecting a strain measuring device to a polished rod of a well pumping unit, and more particularly, to removable apparatus which measures axial strain in a variety of sizes of polished rods irrespective of any bending in the polished rod.
Sucker-rod type pumping units are widely used in the petroleum industry in order to recover fluid from wells extending into subterranean formations. Such units include a sucker-rod string which extends into the well and means at the surface for an up and down movement of the rod string in order to operate a downhole pump. Typical of such units are the so called "beam-type" pumping units having the sucker-rod string suspended at the surface of the well consisting of a Samson post and a walking beam pivotally connected on the Samson post. The sucker-rod string is normally connected to one end of the walking beam by a polished rod and the other end of the walking beam is connected to a prime mover such as a motor through a suitable crank and pitman connection. In this arrangement the walking beam, polished rod and sucker-rod string are driven in a reciprocable mode by the prime mover.
A variety of malfunctions such as worn pumps, broken sucker-rods, split tubing, and stuck pump valves can interrupt the pumping of fluid from a well. Such malfunctions can be caused by normal wear and tear on the equipment, by the nature of the fluid being pumped or they could be caused by abnormal pumping conditions.
A load cell can be connected between the polished rod and the walking beam to measure the axial strain or load on the polished rod. The change in axial strain on the polished rod can be used to detect and analyze the presence of abnormal pumping conditions. However, placing a load cell between the polished rod and the walking beam of each well is not only expensive, but changing such a load cell is expensive, time consuming and there is a risk of dropping a disconnected sucker-rod string into the well.